feat: Add support for JS and TS interfaces/unions

[MorFix]

Description of changes

A PR has added support for unions and interfaces. However, they were still not working for generating models for JS/TS -index.js, index.d.ts, and schema.js metadata file. This PR aims to complete this work and add the necessary support

Codegen Paramaters Changed or Added

N/A

Issue #, if available

N/A

Description of how you validated changes

Updating and adding tests at the moment.

Checklist

• [X] PR description included
• [ ] yarn test passes
• [ ] E2E test run linked
• [ ] Tests are changed or added

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